Top-ranked Victoria Azarenka withdrew from her Brisbane International against Serena Williams with an infected right big toe on Friday, citing concerns about aggravating the injury so close to the Australian Open.

Azarenka made the announcement about a half hour before she was to play the third-ranked Williams, who has an 11-1 record against Azarenka and is on a roll after winning titles at Wimbledon, the London Olympics and the U.S. Open.

It came soon after Andy Murray, the Olympic men's gold medalist and U.S. Open champion, had finished off his 6-4, 7-6 (3) win over Uzbekistan's Denis Istomin in the quarterfinals.

Murray had lapses in his opening three-set win over No. 199-ranked Australian qualifier John Millman on Thursday night, while Ivan Lendl was en route to Australia, but had no serious trouble with his coach in the stands.

The first of Murray's three titles in a breakthrough 2012 season was in Brisbane, where he started working with former No. 1-ranked Lendl last January. The next two titles were career-defining triumphs at the London Olympics and U.S. Open.

Earlier Friday, 2006 Australian Open finalist Marcos Baghdatis ousted No. 3 Gilles Simon of France 6-3, 6-4 to set up a semifinal against Grigor Dimitrov of Bulgaria, who beat seventh-seeded Jurgen Melzer of Austria 6-3, 6-2.

Murray didn't face a break point in the second set, and only lost one point in his first three service games of the set — a call he disputed but lost on the challenge review.

He held serve to force a tiebreaker and trailed Istomin 3-1 before winning six straight points. Istomin served the only double-fault of the match to surrender triple match point and Murray hit a forehand winner to clinch it in little more than 1½ hours.

Murray dropped a set to Millman and appeared to be sore and fatigued at times on Thursday night, but there were no such issues in front of Lendl, who has played a key role in ending the Scottish player's run of four defeats in Grand Slam finals before he finally won a major. Lendl also lost four major finals before his claiming the first of his eight Grand Slam crowns.